1. Field of the Invention
The present invention relates to a transport-by-suction type die for use in a lead working machine useful in the fabrication of semiconductor devices.
2. Discussion of the Related Art
The fabrication of plastic-molded semiconductor devices includes the steps of placing semiconductor chips on to leadframes, molding them with plastics and performing the necessary working processes such as resin removal, dam bar cutting, lead tip cutting and lead forming. The lead working machine is used at this post-die-processing stage to perform lead forming and various other working steps.
The lead working machine is usually operated with more than one die. The working operation is performed in two different ways: in one case, the leadframe is worked or operated on as it is transported in a strip form and piece parts are separated from it at the final stage and in the other case, lead cutting and dam bar cutting are first conducted and then the product portions are separated as piece parts from the leadframe and transported to the bending step. The primary reason for adopting these two different methods of transport is as follows: in the case where the leadframe is transported in a strip form, a simple transport apparatus will do since the top and bottom rails of the leadframe can be utilized as transport guides; however, with product portions that are not suspended from the top and bottom rails by means of hanger pins (i.e., pinch leads for suspending the packages) or with products that are suspended by means of hanger pins but which may drop during transport owing to the insufficient strength of the pins, transport of the leadframe for bending or otherwise working the leads is sometimes impossible unless it is separated into piece parts.
FIGS. 19, 20 and 21 are illustrations showing the layout of a prior art lead working machine. FIG. 19 shows an apparatus that performs working processes up to the bending stage as a leadframe in a strip form is fed consecutively with pins inserted into the rail holes in the leadframe. In this apparatus, the leadframe generally indicated by 5 is worked as it is supplied from the left side of the apparatus into a first die 7 and a second die 8 on a platform 6. A feed unit 10 which allows the leadframe to be fed consecutively with pins inserted into the rail holes is positioned parallel to the train of dies. In the final step following the bending process, piece parts 11 are separated from the product, transported from the second die and replaced in a receiving portion 12. The unwanted frame which remains after the separation of piece parts 11 is directly ejected from the second die to fall free. Depending on the relationship between the number of working processes and the number of chips on the leadframe, three or more dies may be arranged side by side for working the leads.
The working machine shown in FIG. 19 is useful with DIP, ZIP, SOJ, PLCC and all other products that have hanger pins. It is particularly suitable for use with TSOPs which are difficult to effect precise positioning with reference to the lateral sides of thin packages into which the leadframe has been separated.
FIG. 20 shows a working machine that has a first die 7 and a second die 8 arranged in a direction normal to the supply of the leadframe 5. In the first die 7, the leadframe is transported as it is while working processes such as dam bar cutting and lead tip cutting are effected and, at the final stage, the leadframe piece parts are separated from the leadframe; the piece parts then leave the first die 7 in an orthogonal direction and enter the second die 8, through which the piece parts are fed consecutively for further working. In the second die 8, the piece parts are fed consecutively by sliding over the die by means of a feed bar 14 so that the leads are bent successively and thereafter replaced in the receiving portion 12. The unwanted frame 15 is directly ejected from the first die 7. A feed bar transport unit 16 is located parallel to the second die 8.
The working machine shown in FIG. 20 is useful with DIP, ZIP, SOJ, SOP and other products that have outer leads attached in one or two directions. Because of the structural design of the bending die, this type of working machine allows for precise positioning by lateral movement and, hence, it is especially suitable for use with SOP and SOJ.
FIG. 21 shows a case in which the leadframe is transported through a first die 7 as it is while working processes such as dam bar cutting and lead tip cutting are effected and, at the final stage, piece parts 11 are separated from the leadframe; thereafter the piece parts 11 emerge from the first die 7 in a direction normal to the transport through said die and they are successively transported by suction to pass through a second die 17, a third die 18 and a fourth die 19 for working the leads. For transporting the piece parts 11 between successive dies, a suction transport unit 20 is provided parallel to the second die 17, third die 18 and fourth die 19. The apparatus shown in FIG. 21 requires as many dies as the steps of the bending process.
The working machine shown in FIG. 21 is useful with QFP, PLCC and other products that have outer leads attached in four directions. It is particularly suitable for use with QFP and PLCC which are large packages that may drop while they are transported when engaged by means of hanger pins.
As described above, the conventional lead working machines have a plurality of die units set in such a way that the work is transported from one die to the next during consecutive working. In the case shown in FIG. 21, piece parts are separated from the leadframe in the first die and, thereafter, each part 11 is supported by suction and successively transported to dies 17, 18 and 19 for performing the necessary working processes.
This method of transport by suction is used with semiconductor products that are large packages and which may drop while they are transported when engaged by means of hanger pins. Conventional working machines that rely upon transport by suction have a suction transport unit 20 on the side lateral to the train of dies (see FIG. 21) so that each piece part is moved from one die and replaced on the next die. The transport unit 20 has feed arms that are located in the retracted positions lateral to the dies 17, 18 and 19 and which get into the space between dies in each working process to transport the piece part. Therefore, the conventional working machines must use different dies for different working processes and the suction transport unit 20 is installed to match these dies.
Under these circumstances, setting dies in the conventional working machines has been cumbersome or the need has existed to manufacture dies to different specifications. Other problems that have been encountered are as follows: If many die units are to be used, the number of feed arms will increase and the inevitable increase in the weight of the moving parts will limit the efforts to increase the indexing speed; the feed arms in the conventional working machine is cantilevered, so if they are moved at higher speeds, their tip will vibrate and the product which is being set in a working die cannot be placed into a pocket precisely and this occasionally results in a broken product or a damaged dies; to increase the indexing speed with the conventional working machine, the posts on the side where the feed arms are provided are omitted, thereby insuring the reciprocal movements of the feed arms but, then, the mounting strength of the upper and lower parts of each die is insufficient to insure satisfactory positional precision; and the strokes of the upper and lower parts of each die will increase to prevent the efforts to increase the indexing speed in an effective way.